This invention pertains to vessels for containing molten metal, for example steel making ladles, and particularly to the refractory lining for such vessels.
Some years ago it was customary to line steelmaking ladles with refractory brick made from clays which had the characteristic that, at the temperatures encountered in use, the brick expanded or "bloated" so as to wedge themselves within the ladle and close very tightly any joints between the brick. However, one shortcoming of such brick is their relatively low refractoriness.
As the temperatures of molten steel in steelmaking operations have increased in more recent years, and the time of holding metal in a ladle, for example to refne it, has increased, it has become the practice to line the ladles with more refractory brick, for example high alumina brick.
Even more recently it has become the practice to line steelmaking ladles with so-called "basic" brick, that is to say brick made with materials such as periclase and combinations of periclase and chrome ore, particularly when the ladle slag is a basic slag. There are many kinds of such basic refractories, varying in their composition and method of manufacture (e.g., whether chemically bonded or fired).
The term "basic" as used in connection with both refractories and slags refers to their chemical composition. Thus, for example MgO- and CaO-containing compositions, either refractory brick or slag, are considered "basic" because of the chemical nature of these materials, whereas silica, for example, on the other hand, again either in the molten form in slag or in the solid form in refractory brick, is considered an "acid" material. Generally, the chemical nature of these materials is such that one basic material tends to react relatively slowly with another basic material, but will react chemically very rapidly with an acid material.
The refractories in a steelmaking ladle wear mainly by corrosion and erosion, although thermal shock may play a role, and there is a continual search for a refractory which will have a longer life in the ladle, particularly with respect to its cost. In other words, the steelmaker is looking for a refractory that will cost the least number of dollars per ton of steel produced.
As is customary in many refractories applications, it is a frequent practice to use a higher grade of refractory in areas of greater wear. In a steelmaking ladle, this is generally the area known as the "slagline", that is to say the level in the vessel where the slag comes in contact with the refractory lining when the vessel is filled with molten metal. Accordingly, a more erosion/corrosion resistant refractory is sought for this particular area.
The present invention relates to a refractory lining which has proven to be outstandingly resistant to corrosion and erosion by a basic slag in a steelmaking ladle, particularly at the slag line.